(1) Field of the Invention
This invention relates to a catalyst for hydrogenation or selective demetallization treatment of hydrocarbons, which comprises one or more of metals selected from the group consisting of transition metals and metals of group IIb of the periodic table supported on sepiolite, and the method for preparation of said catalyst as well as the process for the hydrogenation and demetallization in the presence of said catalyst under a hydrogen pressure and at a high temperature.
(2) Description of the Prior Art
Impurities such as sulfur, nitrogen and metals are contained in the hydrocarbons including crude oils, heavy oils, cracked oils, deasphalted oils, topped residual oils, vacuum gas oils, tar sands, bitumens, shale oils, or the mixtures thereof. These impurities are discharged into the atmosphere together with the exhaust gas when these hydrocarbons are subjected to combustion, becoming a source of the environmental pollution. Also, the soluble metals contained in the hydrocarbons are deposited on a catalyst in the catalytic treatment of hydrocarbons, causing a marked decrease in the catalytic activity of the catalyst and the selectivity of the reaction. Therefore, in order to utilize the hydrocarbons as a harmless energy source or as the starting material in a catalytic process, it is necessary to remove sulfur, nitrogen and metals from them beforehand. Above all, it is becoming an indispensable requisite that the metals are removed previous to the treatment of non-metallic impurities such as sulfur and nitrogen. Since these metals were, heretofore, simultaneously treated together with sulfur, nitrogen and the like without subjecting to any pretreatment, it was necessitated to use the catalyst in an amount in large excess to the theoretical amount required for desulfurization or denitridication. But as the catalysts for these desulfurization and denitrification are very expensive the development of an inexpensive catalyst which is excellent in demetallization characteristic has been desired.
In the prior art, when demetallization treatment is carried out beforehand, hydrocarbons are treated by utilizing either an ordinary desulfurization catalyst or a waste catalyst having almost no desulfurization activity, or using bauxite, red mud and the like as the catalyst in the so-called guard reactor. All these catalysts, however, have defects in that the activity of demetallization is low or the life time of the catalysts is too short, and moreover, they are very unsatisfactory for the purpose of carrying out a selective and effective demetallization reaction.
In the case of a catalyst having a relatively high demetallization activity, usually the desulfurization reaction also proceeds simultaneously, and as a result this often causes trouble in the utilization of the hydrocarbons thus demetallized. For example, red mud is available at a very low price and in quantities and is a useful catalyst for demetallization having the activity of removing, under a high hydrogen pressure, the metals contained in hydrocarbon oils, especially vanadium, nickel and iron. But, it has defects in that the demetallization treatment must be carried at high temperatures requiring a very long contact time. The oils treated in the presence of the red mud-catalyst is extremely instabilized as a result of a long residence time at a high temperature, and further it may happen that carbonaceous substances are caused to be deposited to clog the reactor near the exit of the catalyst layer. In order to avoid such trouble the treatment may be carried out at a relatively low temperature, but it takes a still longer time and is very disadvantageous from an economical viewpoint because of the necessity of providing .[.a large-sized reaction.]. .Iadd.large-sized reactor .Iaddend..
Bauxite is also available at a price as low as that of red mud and has a demetallization activity higher than that of red mud. But bauxite has defects in that the lowering in the activity is considerably large on account of its small pore volume and the life time of catalyst is short. A catalyst having such a small pore volume as bauxite is not suitable for the treatment of hydrocarbons containing a high content of metals.
Incidentally, the demetallization reaction of hydrocarbons is the so-called hydrogenation reaction which is carried out in the presence of catalyst under a hydrogen pressure and at a high temperature. It has been known for a long time that the demetallization reaction takes place together with a desulfurization reaction since metals are deposited on a catalyst in the course of the desulfurization reaction. In the desulfurization treatment using a conventional desulfurization catalyst, the higher the desulfurization ratio is raised, the higher the demetallization becomes, and the desulfurization and demetallization reactions take place in an almost definite proportion under the same condition. On the contrary, even when demetallization is carried out by using a conventional desulfurization catalyst, it is totally impossible to avoid the desulfurization reaction which takes place in the definite proportion. These phenomena will be further studied in comparison with the effects obtained by the present invention in the following.